In a conventional on-board unit, if dust enters the unit through an opening provided in the unit, a mechanical or optical component inside the unit might go out of order, causing the unit to malfunction.
In order to address this problem, in an IC card terminal with a card insertion slot for insertion of an IC card, the card insertion slot is lined with a card insertion slot cover so as to prevent dust from entering the IC card terminal through the card insertion slot (for example, see Japanese Patent Document No. JP-A-H06-333100). In addition to this type of unit, various dust prevention techniques have been proposed (for example, see Japanese Patent Documents No. JP-A-2001-020320, JP-A-2003-302620, JP-A-2005-203592, and U.S. Pat. No. 5,822,192, and European Patent Document No. EP 1479603A2).
Some types of audio visual navigation systems have a deck slot 17a into which a medium such as a CD, DVD or MD is inserted as shown in FIG. 7. Other types of audio visual navigation systems have a deck slot 17a into which a medium such as a CD, DVD or MD is inserted, and a tilt panel 19 on the front of the unit, as shown in FIG. 8 and are structured so that as the tilt panel 19 is moved, a deck slot 18a for insertion of a medium storing map data appears as shown in FIG. 9.
These systems have the problem that if there is dust including a cloud of sand inside the vehicle compartment, dust enters the unit through the deck slot 17a as a medium is loaded or unloaded.
Also, in the unit with the tilt panel 19 as shown in FIG. 8, if the vehicle is running, with the tilt panel open as shown in FIG. 9, in an area where there is much dust including a cloud of sand, dust might enter the unit through the deck slot 18a behind the tilt panel 19 or a gap such as an opening through which a tilt bar 20a for moving the tilt panel 19 is passed.
If dust enters the unit in this way, it might cause rotation trouble of the motor inside the unit or operation trouble of the tilt mechanism for moving the tilt panel. In addition, dust might adhere to the optical lens of the laser pickup inside the unit, resulting in deterioration of the laser scanning performance, detection errors or similar problems.
It is difficult to apply the dust prevention measures as described in JP-A-H06-333100 to the above audio visual navigation systems because the card insertion slot cover might cause such a problem as deterioration of the laser scanning performance. Similarly, it is difficult to apply the techniques indicated in Japanese Patent Documents No. JP-A-2001-020320, JP-A-2003-302620, JP-A-2005-203592, and U.S. Pat. No. 5,822,192, and European Patent Document No. EP 1479603A2 to on-board audio units or audio visual navigation systems as described above.